1. Field of the Invention
The present invention relates to a synchronization apparatus that synchronizes the operation of a plurality of processing units performing signal processing, and to a field device having the apparatus.
Priority is claimed on Japanese Patent Application No. 2012-068040, filed Mar. 23, 2012, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
Conventionally, in order to implement a high level of automated operation in plants, factories, and the like, distributed control systems (DCSs) have been implemented, in which on-site equipment (measuring instruments and actuators) known as field devices are connected to controllers that control the field devices via a communication means. In these distributed control systems, measurement data such as flow amount, pressure, temperature, humidity (physical quantities) measured by the field devices are collected by the controllers and the field devices are operated (controlled) by the controllers in response to the collected measurement data, thereby adjusting the flow amount and the like.
Of the above-noted field devices, the field devices that can measure flow amount and the like, are generally are constituted so as to have a detection unit that detects a fluid or the like, a signal processing unit that subjects the detection signal from the detection unit to signal processing to determines the flow amount or the like, and an output unit that outputs to the outside as measurement data the result of the processing by the signal processing unit. The above-noted signal processing unit is often divided into a pre-established processing unit that subjects the detection signal from the detection unit to pre-processing such as filtering, and a post-processing unit that subjects the signal processed by the pre-processing unit to post-processing to determine the flow amount or the like, and that also controls the output unit.
A conventional field device is generally an analog transmission type in which an output unit is connected to an analog transmission line (for example a transmission line used to transmit a 4 to 20 mA signal), converts the processing results from the signal processing unit to an analog signal and outputs the analog signal to the analog transmission line. In contrast, in recent years, hybrid transmission type (smart transmission type) field devices that can superimpose a digital signal onto an analog signal, and transmit the analog signal and the digital signal on an analog transmission line have come into use. Japanese Unexamined Patent Application, First Publication No. 2010-134752 discloses a field device capable of switching between analog transmission and hybrid transmission.
In a field device, because the detection unit is electrically connected to the object under detection (for example, a fluid or a pipe through which a fluid flows), electrical insulation is required between the output unit that is connected to an external apparatus (for example, a controller) and the detection unit. In a field device of the analog transmission type described above, because an analog signal responsive to the processing result of the signal processing unit (post-processing unit) is merely output from the output unit to the analog transmission line, there is almost always electrical insulation between the signal processing unit (post-processing unit) and the output unit.
In contrast to this, a field device of the hybrid transmission type described above superimposes a digital signal onto an analog signal responsive to the processing result of the signal processing unit (post-processing unit) and outputs the result. For this reason, in a field device of the hybrid transmission type, if electrical insulation is provided between the signal processing unit (post-processing unit) and the output unit, it is necessary to insulate not only the path via which the processing result of the signal processing unit (post-processing unit) is input to the output unit, but also the path via which the digital signal (digital signal that is superimposed onto the analog signal) is input to the output unit, and there is the problem of an increase in cost.
Given this, in the above-described hybrid transmission type field device, it can be envisioned that the above-described increase in cost will not occur if the electrical insulation is provided between the pre-processing and post-processing units of the signal processing unit. In a field device, however, it is necessary synchronize the detection of the fluid in the detection unit, the signal processing in the signal processing unit, and the output in the output unit with the timing of the measuring the flow amount or the like. If the pre-processing and post-processing units of the signal processing unit are electrically insulated, there is the problem of noise intruding via the insulation circuit, or drop-out of the signal occurring in the insulation circuit causing a worsening of the accuracy of synchronization between the pre-processing and post-processing units of the signal processing unit. These problems occur not only when the pre-processing unit and the post-processing unit are connected via an insulation circuit, but also when connection is made via a connection line such as a transmission line onto which the superimposition of noise or signal drop-out can occur.